I don't know if my method is the best, but is sure is the cheapest and very easy. I am not keeping the original ceiling and I had all these stainless steel panels left over from ripping the ceiling out, so I just cut them down to fit, calked between the bus and panel real good and used plenty of fasteners, I also added some additional bracing to help stiffen the panels. I don't know if I would have enough to cover all the windows, but I have enough to do the ones I am eliminating. I will let you know in a couple of years how they are holding up

Aluminum, steel, stainless steel, fiberglass. I think between all the manufactures they have used them all. Aluminum is light, but unless its 1/8th inch it gets wavy. With any material, thickness increases rigidity.

The glass is real heavy safety glass like a car windshield. We once threw all the glass from a fishbowl into a dumpster, the garbage truck couldnt lift it. He estimated it was nearly 1 ton. That sounds like a lot, but each side glass took two guys to lift down, they are not light, and there are 8 to 10 of them in a Bus, plus the windshield, back glass, and front driver side and door glass.

My plan is to keep the window frames but replace the glass with lexan or some kind of polycarbonate, or possibly aluminum panels. That will keep it looking like a Bus, but it will lose a lot of weight. If I screw them down from the outside I wont have any trouble doing repairs.